I've been in Mexico for a month and a half and I'm currently heading to Mexico City to apply for a Chinese visa since I already have a flight back to China but my previous visa expired.
China requires a minimum of three bookings to issue a visa: One flight to China, One flight out of China, and one accommodation booking. Even if you intend to enter and/or leave via a land border and even if you're applying for a double-entry visa you only need show these reservations for the first entry.
Previously I have done this in Laos and Australia. In Vientiane one travel agent understood exactly what I needed and made the bookings, printed them out, then cancelled them for just a few dollars. In Australia a friend who worked as a travel agent at the time booked my flights and sent me the bookings before cancelling them.
In Mexico City I don't have such a friend and where you can walk around every travel agency in Vientiane in less than an hour, Mexico City is one of the biggest cities in the world.
I know I can book some kind of flight with no or low cancellation fee myself but don't know how to find such flights. There might be other ways I never thought of.